This invention relates to a distributor for an internal combustion engine, and in particular to a distributor for suppressing radio frequency interference or radio noise (hereinafter referred to as RFI) which is generated between a rotor electrode and a lateral terminal electrode forming the distributor in the ignition system of an internal combustion engine. This invention also relates to a method of making the rotor electrode used in such a distributor.
A conventional distributor for an internal combustion engine is shown in FIG. 1. A distributor rotor electrode 10 molded in a distributor rotor 11 is positioned to face a lateral terminal electrode 12 through a discharging gap "g". FIG. 1 only shows a single lateral terminal electrode 12, but actually the distributor has a plurality of lateral terminal electrodes corresponding to the number of cylinders of an engine (not shown). A contact electrode 14 makes contact with the rotor electrode 10 and supplies a high voltage from an ignition coil (not shown) to the rotor electrode 10 through a secondary high-tension cable 16. The contact electrode 14 is pressed, with a spring 18, against the rotor electrode 10 rotated by a rotary axle 20 interconnected to the crank-shaft of an internal combustion engine. A dielectric material 22 mainly formed of silicon is coated entirely on the discharging end, i.e. the periphery end of the rotor electrode 10.
In operation, when a high voltage is supplied to the rotor electrode 10 through the high-tension cable 16 and the contact electrode 14, the dielectric material 22 serves to increase the emission of electrons from the rotor electrode 10 towards the lateral terminal electrode 12 to start a discharge at a voltage lower than a usual breakdown voltage in the discharge gap "g". This reduction of the breakdown voltage in the discharge gap suppresses the generation of the RFI.
However, in the presence of the silicon dielectric material 22 fully coated on the discharging end of the rotor electrode 10, intermittent discharges arise due to charged particles accumulated in the dielectric material 22 during the induced discharge, whereby a sufficient effect for suppressing the RFI is not attained. Furthermore, being exposed to the discharge, the silicon dielectric material 22 is easily exfoliated and dropped from the end of the rotor electrode 10 so that it can not retain the RFI suppressing effect for long periods of time, resulting in a poor durability and operability. Also, since the dielectric material 22 is coated on the top end of the rotor electrode 10 one at a time, the dielectric material 22 is not practical from the view of the mass-production thereof.
On the other hand, a published article tilted "Suppression of Radio Frequency Interference at the Distributor Rotor Gap" (IEEE Trans. Vehicular Technology Vol. 1, VT-28, No. 2, May 1979) by Wey-Chang Kuo discloses that when a dielectric material is disposed at the rotor segment, the RFI and breakdown voltage is greatly reduced. The dielectric material may comprise compounds of silicon oxide, zinc oxide, glass, and various ceramics.